1. Technical Field of the Invention
The present invention relates to a method and apparatus for varying the tobacco density over the length of a tobacco rod product such as a cigarette.
2. Discussion of the Related Art
A cigarette may be produced composed wholly or in part of expanded shreds of tobacco and/or of expanded ribs of tobacco. These ingredients are present in the form of small shreds which are more difficult to work than the usual long shreds of leaf tobacco. A cigarette of this type, obtained by a usual manufacturing process, will have a low value of filling density, i.e., a poor maintenance of tobacco in the cigarette. If, in order to increase this filling density to a favorable value, the tobacco is squeezed more or its cramming is increased, a cigarette is obtained having modified characteristics such as resistance to draw or yield.
The problems mentioned above are the same when the cigarette includes a certain proportion of non-expanded short shreds of tobacco. These short shreds are either chosen to form part of a particular mixture of tobacco or result from damaging the shreds of tobacco at the time of the earlier preparation operations.
The compactness of the finished product is checked by a compressibility-measurement apparatus as described in European patent EP-A-0,195,173.